The present invention relates to a parallel shaft transmission, in which a plurality of gear trains are provided to connect a plurality of shafts that are disposed parallel with one another, and a plurality of clutching means are provided each to be engaged selectively with a corresponding one of the gear trains to establish a power transmission path.
Such parallel shaft transmissions are widely used in automobiles. For example, an automatic transmission with five speed ratios has been disclosed in Japanese Laid-Open Patent Publications No. 4(1992)-331852 (A), No. 5 (1993)-272601 (A) and No. 7 (1995)-19295 (A).
In this transmission, a plurality of gear trains are arranged over a plurality of shafts which are disposed in parallel with one anther, and these gear trains are disposed axially parallel with one anther. In addition, a plurality of clutches are provided each close to a respective gear train for the purpose of selecting that specific gear train for mechanical power transmission. Because of this arrangement, generally, the axial dimension of the transmission is relatively large. This tendency of the transmission having a large axial dimension becomes more prominent as the number of available speed ratios is increased in the design of the transmission. Especially, automatic transmissions are prone to acquiring a large size because they typically include hydraulic clutches, whose dimensions in radial direction as well as in axial direction are relatively large.
Nowadays, transmissions which are used in automobiles are equipped with a large number of speed ratios to improve drive performance, and the number of speed ratios has increased from three to four. Now, a transmission with five speed ratios is coming to be practical, so the size of the transmission is becoming a serious problem because the transmission, which has such a large number of speed ratios, acquires a correspondingly large size. In the automatic transmission with five speed ratios which has been disclosed in the above mentioned publications, various ideas are applied in the arrangement of the gears and the clutches to minimize the size of the transmission.
It is an object of the present invention to provide a parallel shaft transmission which incorporates a large number of speed ratios in a construction designed as compact as possible by contriving an arrangement for integrating gears and clutches.
In order to achieve this objective, the present invention provides a parallel shaft transmission comprising a first input shaft, a second input shaft, and a counter shaft, which are disposed parallel with one another. This transmission further comprises at least one set of first speed ratio gear train (for example, the fifth speed gear train 25a and 25b, the fourth speed gear train 24a and 24b and the reverse gear train 26a, 26b and 26c of the following embodiment shown in FIG. 3), at least one first clutching means (for example, the fifth speed clutch 15 and the fourth speed clutch 14 of the embodiment shown in FIG. 3), at least one set of second speed ratio gear train (for example, the second speed gear train 22a and 22b, the LOW gear train 21a and 21b and the third speed gear train 23a and 23b of the embodiment shown in FIG. 3), at least one second clutching means (for example, the second speed clutch 12, the LOW clutch 11 and the third speed clutch 13 of the embodiment shown in FIG. 3), and a connection gear train. Each set of first speed ratio gear train includes a first speed ratio drive gear (for example, the fifth speed drive gear 25a, the fourth speed drive gear 24a and the reverse drive gear 26a of the embodiment shown in FIG. 3) which is disposed on the first input shaft and a first speed ratio driven gear (for example, the fifth speed driven gear 25b, the fourth speed driven gear 24b and the reverse driven gear 26c of the embodiment shown in FIG. 3) which is disposed on the counter shaft, with the first speed ratio drive gear and the first speed ratio driven gear meshing with each other. The first clutching means is disposed on the first input shaft, and it connects and disconnects the first speed ratio drive gear rotationally to and from the first input shaft, respectively. Each set of second speed ratio gear train includes a second speed ratio drive gear (for example, the second speed drive gear 22a, LOW drive gear 21a and third speed drive gear 23a of the embodiment shown in FIG. 3) which is disposed on the second input shaft and a second speed ratio driven gear (for example, the second speed driven gear 22b, the LOW driven gear 21b and the third speed driven gear 23b of the embodiment shown in FIG. 3) which is disposed on the counter shaft, with the; second speed ratio drive gear and the second speed ratio driven gear meshing with each other. The second clutching means is disposed on the second input shaft, and it connects and disconnects the second speed ratio drive gear rotationally to and from the second input shaft, respectively. The connection gear train is used for power transmission from the first input shaft to the second input shaft through a gear (for example, the second and third connection gears 32 and 33 of the embodiment shown in FIG. 3) on an idle shaft which is disposed parallel with the first input shaft.
In this parallel shaft transmission, the drive power which is input from the engine to the first input shaft can be transmitted through the connection gear train directly to the second input shaft. As the speed ratio gear trains are disposed between the first input shaft and the counter shaft as well as between the second input shaft and the counter shaft, the axial length of the transmission is relatively short, so the transmission is made compact. Also, because the connection gear train includes a gear which is disposed on an idle shaft, the distance between the first input shaft and the second input shaft is adjustable as desired. Therefore, the clutching means which comprise hydraulic clutches, whose dimensions in radial direction are relatively large, do not interfere with each other even though the first clutching means, which is disposed on the first input shaft, and the second clutching means, which is disposed on the second input shaft, are positioned substantially on a common plane which is perpendicular to the shafts. There is a high degree of freedom in the arrangement of the clutching means. As a result, the first and second speed ratio gear trains and the first and second clutching means are arranged appropriately to construct the transmission in a relatively small size.
It is preferable that the connection gear train comprise a first connection gear which is mounted on the first input shaft, a second connection gear and a third connection gear which are disposed on the idle shaft and a fourth connection gear which is mounted on the second input shaft. In this case, the first connection gear meshes with the second connection gear; the second connection gear and the third connection gear rotate together as a unified body; and the third connection gear meshes with the fourth connection gear. In this construction, only the second and third connection gears, which rotate together as a unified body, are provided on the idle shaft. Thus, bearings can be disposed adjacent to these gears to support the idle shaft so as to restrict deformation of the idle shaft, which deformation may otherwise occur during the power transmission under a heavy load. Therefore, the meshing of the connection gears which are supported by the idle shaft is not affected from changes in the load of the transmission. As a result, the noise of the meshing is controlled to a relatively low level. Furthermore, because the design is such that the first connection gear meshes with the second connection gear while the third connection gear meshes with the fourth connection gear, the tooth surfaces which are located on one side in each connection gear are used for the acceleration while those located on the other side are used for the deceleration. Therefore, the tooth surfaces can be modified independently for the acceleration and for the deceleration to reduce the meshing gear noise.
Preferably, one of the second clutching means (for example, the second speed clutch 12 of the embodiment shown in FIG. 3) and an output gear (for example, the last reduction drive gear 6a of the embodiment shown in FIG. 3) which is mounted on the counter shaft are positioned substantially on a plane which is perpendicular to the shafts. The output gear train is used as the last reduction gear train, so it has a comparatively large reduction ratio. Thus, the output gear (last reduction drive gear) has a small diameter. Generally, the space surrounding the output gear tends to become a dead space in transmission design. However, in this transmission, this space, which may be a dead space otherwise, is utilized for incorporating the second clutching means. Therefore, the second clutching means is disposed substantially in the same plane as the output gear, to make the transmission compact.
This transmission can be constructed as a five speed ratio transmission. In this case, preferably, the first speed ratio gear train comprises a fourth speed gear train and a fifth speed gear train; the first clutching means comprises a fourth speed clutch and a fifth speed clutch; the second speed ratio gear train comprises a LOW gear train, a second speed gear train and a third speed gear train; and the second clutching means comprises a LOW clutch, a second speed clutch and a third speed clutch. Furthermore, it is preferable to provide a reverse gear train including a reverse drive gear, which is disposed on the first input shaft, and a reverse driven gear, which is disposed on the counter shaft. In this case, the reverse drive gear is rotationally connected with the reverse driven gear through a reverse idler gear, which rotates around a shaft that is provided parallel with the first input shaft. In addition, the reverse drive gear and the fourth speed drive gear, which is a component of the fourth speed gear train, are couple with each other as one body and are disposed rotatably on the first input shaft, such that the reverse drive gear and the fourth speed drive gear are connected and disconnected rotationally to and from the first input shaft by the fourth speed clutch, respectively. On the other hand, the fourth speed driven gear, which is the other component of the fourth speed ratio gear train, and the reverse driven gear are each disposed rotatably on the counter shaft, and a dog clutch is provided on the counter shaft, such that the fourth speed driven gear and the reverse driven gear are selectively connected and disconnected to and from the counter shaft, respectively.
In this way, a compact five speed transmission capable of establishing five forward speed ratios and one reverse speed ratio is realized according to the present invention. Especially in the above mentioned arrangement, at first, either the fourth speed driven gear or the reverse driven gear is connected rotationally to the counter shaft by the dog clutch to establish the forward drive range (D range) or the reverse drive range (R range), respectively, and then the fourth speed clutch is engaged to establish the fourth speed ratio or the reverse speed ratio, correspondingly. Here, the fourth speed clutch is used both for establishing the four speed ratio and for establishing the reverse speed ratio. There is another advantage in this arrangement. If the fifth speed gear train is removed to construct a four speed transmission, then the fourth speed clutch, as it is, is still usable for establishing the four speed ratio and the reverse speed ratio.
A second embodiment of parallel shaft transmission according to the present invention comprises a first input shaft, a second input shaft, a first counter shaft and a second counter shaft, which are disposed parallel with one another. This transmission further comprises at least one set of first speed ratio gear train (for example, the fourth speed gear train 74a and 74b, the fifth speed gear train 75a and 75b and the reverse gear train 76a and 76c of the embodiment shown in FIG. 11), at least one first clutching means (for example, the fourth speed clutch 64 and the fifth speed clutch 65 of the embodiment shown in FIG. 11), at least one set of second speed ratio gear train (for example, the third speed gear train 73a and 73b, the LOW gear train 71a and 71b and the second speed gear train 72a and 72b of the embodiment shown in FIG. 11), at least one second clutching means (for example, the third speed clutch 63, the LOW clutch 61 and the second speed clutch 62 of the embodiment shown in FIG. 1) and a connection gear train (for example, the connection gear train 80 of the embodiment shown in FIG. 11). In this case, each set of first speed ratio gear train includes a first speed ratio drive gear (for example, the fourth speed drive gear 74a, the fifth speed drive gear 75a and the reverse drive gear 76a of the embodiment shown in FIG. 11) which is disposed on the first input shaft and a first speed ratio driven gear (for example, the fourth speed driven gear 74b, the fifth speed driven gear 75b and the reverse driven gear 76c of the embodiment shown in FIG. 11) which is disposed on the first counter shaft, with the first speed ratio drive gear and the first speed ratio driven gear meshing with each other. The first clutching means is disposed on the first input shaft, such that it connects and disconnects the first speed ratio drive gear rotationally to and from the first input shaft, respectively. Each set of second speed ratio gear train includes a second speed ratio drive gear (for example, the third speed drive gear 73a, the LOW drive gear 71a and the second drive gear 72a of the embodiment shown in FIG. 11) which is disposed on the second input shaft and a second speed ratio driven gear (for example, the third speed driven gear 73b, the LOW driven gear 71b and the second speed driven gear 72b of the embodiment shown in FIG. 11) which is disposed on the second counter shaft, with the second speed ratio drive gear and the second speed ratio driven gear meshing with each other. The second clutching means is disposed on the second input shaft, such that it connects and disconnects the second speed ratio drive gear rotationally to and from the second input shaft, respectively. The connection gear train is used for power transmission from the first input shaft to the second input shaft through a connection idle gear (for example, the second connection gear 82 of the embodiment shown in FIG. 11), which is provided rotatably on the first counter shaft. In this construction, transmission output is taken out from first and second output gears (for example, the first and second last reduction drive gears 56a and 56b of the embodiment shown in FIG. 11), which are mounted on the first and second counter shafts, respectively.
In this parallel shaft transmission, the drive power which is input from the engine to the first input shaft can be transmitted through the connection gear train directly to the second input shaft. As the speed ratio gear trains are disposed between the first input shaft and the first counter shaft as well as the second input shaft and the second counter shaft, the axial length of the transmission is relatively short, so the transmission is made relatively compact. Also, because the distance between the first input shaft and the second input shaft can be determined as desired, the clutching means do not interfere with each other even though the first clutching means, which is disposed on the first input shaft, and second clutching means, which is disposed on the second input shaft, are positioned substantially on a common plane which is perpendicular to the shafts. As a result, the first and second speed ratio gear trains and the first and second clutching means are arranged appropriately to construct the transmission in a relatively small size.
As mentioned previously, the first and second output gears (last reduction drive gears) have small diameters. Generally, the space surrounding these output gears tends to become a dead space in transmission design. However, according to the present invention, this space of the transmission, which may be a dead space otherwise, is utilized for incorporating the second clutching means. In other words, one of the second clutching means and the first and second output gears are positioned substantially on a common plane which is perpendicular to the shafts to make the transmission compact.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.